Princeton's WordNet

1. three, 3, III, trio, threesome, tierce, leash, troika, triad, trine, trinity, ternary, ternion, triplet, tercet, terzetto, trey, deuce-ace(noun)

   the cardinal number that is the sum of one and one and one

   Antonyms:
   ordinal

   Synonyms:
   lead, third, tether, trio, collar, one-third, ternary, deuce-ace, tierce, trinity, triplet, terce, triple, threesome, triad, trine, troika, ternion, tercet, trey, leash, terzetto, three, common chord

2. trey, three(adj)

   one of four playing cards in a deck having three pips

   Antonyms:
   ordinal

   Synonyms:
   tierce, trine, trio, ternary, leash, threesome, three, ternion, tercet, triplet, terzetto, deuce-ace, triad, troika, trey, trinity

3. three, 3, iii(adj)

   being one more than two

   Antonyms:
   ordinal

   Synonyms:
   three, iii